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采用金相显微镜及扫描电镜对VAR法制备V-5Cr-5Ti合金样品进行显微组织观察。观察分析了V-5Cr-5Ti合金铸锭、均匀化热处理、塑性变形及再结晶热处理对合金显微组织的影响,特别对合金中生成第二相的演变规律进行了研究。研究发现,V-5Cr-5Ti合金铸锭中的第二相为薄片状,紧密排列呈不规则曲线。铸态第二相具有热稳定的相结构,其分布与合金基体存在一定的择优取向,通过片状第二相之间的取向关系表现出来。1100℃保温2 h均匀化热处理后,第二相的数量和分布发生变化,但不能完全消除。加工过程中合金表现出良好的可加工性能,第二相的偏聚导致合金硬化区的存在,不利于合金的均匀变形,加大变形量(>60%)有助于消除这一影响。变形过程中第二相不发生弹/塑性变形,变形量较大(>80%)时发生破碎,形成细小的颗粒状第二相。变形合金经过800℃保温1 h处理后组织中出现了再结晶的形核,1000℃保温1 h处理后基体中发现了晶粒的长大。第二相的存在提高了合金的再结晶能垒,使其分布区域的再结晶过程滞后于合金基体,导致细晶带的产生,有利于合金的高温力学性能。
The microstructure of V-5Cr-5Ti alloy prepared by VAR method was observed by metallographic microscope and scanning electron microscope. The effects of homogenization heat treatment, plastic deformation and recrystallization heat treatment on the microstructure of V-5Cr-5Ti alloy ingot were investigated. The evolution of the second phase in the alloy was also investigated. The study found that V-5Cr-5Ti alloy ingot in the second phase is flaky, closely arranged irregular curve. The as-cast second phase has a thermostable phase structure with a preferred orientation of distribution to that of the alloy matrix, as evidenced by the orientation of the second phase in the sheet. After heat treatment at 1100 ℃ for 2 h, the number and distribution of the second phase changed but could not be completely eliminated. The processing of the alloy showed good machinability, segregation of the second phase leads to the existence of alloy hardening zone is not conducive to the uniform deformation of the alloy, increase the deformation (> 60%) helps to eliminate this effect. The deformation of the second phase does not occur when the elastic / plastic deformation, large deformation (> 80%) occurs when broken, the formation of small granular second phase. After deformation treatment at 800 ℃ for 1 h, the recrystallized nuclei appeared in the microstructure, and the grain growth was observed in the matrix treated at 1000 ℃ for 1 h. The presence of the second phase increases the recrystallization barrier of the alloy, causing the recrystallization process in its distribution region to lag behind the alloy matrix, resulting in the production of fine crystalline zone, which is in favor of the high temperature mechanical properties of the alloy.